#include <bits/stdc++.h>
using namespace std;
#define int long long
#define fastIO() ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0)
const int mod = 1E9 + 7;
int _hash(string s) {
int p = 257, mod = 13302843816923LL;
int ans = 0;
for (auto c : s) ans = (ans * p + c) % mod;
return ans;
}
int32_t main() {
int n, k;
cin >> n >> k;
string all[n][k];
int hashes[n][k][3]; /// prefix, suffix, all
for (int i = 0; i < n; ++i) {
for (int j = 0; j < k; ++j) {
cin >> all[i][j];
hashes[i][j][2] = _hash(all[i][j]);
if (!i) continue;
hashes[i][j][0] = _hash(all[i][j].substr(0, i));
hashes[i][j][1] = _hash(all[i][j].substr(1));
}
}
int dp[n][k];
for (int i = 0; i < n; ++i) memset(dp[i], 0x00, sizeof(dp[i]));
for (int j = 0; j < k; ++j) dp[0][j] = 1;
for (int i = 1; i < n; ++i) {
for (int j2 = 0; j2 < k; ++j2) {
for (int j1 = 0; j1 < k; ++j1) {
if (hashes[i][j2][0] == hashes[i-1][j1][2] or hashes[i][j2][1] == hashes[i-1][j1][2]) {
dp[i][j2] += dp[i-1][j1];
}
}
dp[i][j2] %= mod;
}
}
int ans = 0;
for (int j = 0; j < k; ++j) ans += dp[n-1][j];
cout << ans%mod << "\n";
return 0;
}
